Judge Masipa found Pistorius guilty of homicide in 2014, and he served less than a year behind bars.

But state prosecutor Gerrie Nel is appealing, arguing Masipa's decision was wrong.

"The court should have rejected his evidence because he was a poor witness. Then all that remains is objective facts. Under objective facts, the accused cannot escape the conviction of murder," Nel told the court Tuesday.

The Guardian sums up the prosecution's argument: "The state must argue not on points of fact, but on points of law — that the high court in its original verdict misapplied or misinterpreted legal principles." (Video via CCTV)

Culpable homicide is a lesser charge than murder, with the main difference being negligence. Pistorius claims he mistook Steenkamp, his then-girlfriend, for an intruder and shot her through the bathroom door.